Process control system having dual wireless communication links

ABSTRACT

Field devices or other devices within a process control system are provided with both hardwired and wireless communication ports to enable communications to be performed within the process control system using one or both of hardwired and wireless communications. In particular, a field device for use in a process control system within a process control environment includes a microprocessor-based communication unit adapted to generate or receive communication signals, a first communication port adapted to be connected to a hardwired communication link for providing communications to or from the communication unit via the hardwired communication link and a second communication port adapted to be connected to a wireless transceiver to provide wireless communications to or from the communication unit via the wireless transceiver.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of pending U.S. application Ser. No.10/961,172, filed Oct. 8, 2004 and entitled “Process Control SystemDevices with Dual Hardwired and Wireless Communication Ports”, and whichwill issue as U.S. Pat. No. 7,623,479 on Nov. 24, 2009 (which is herebyexpressly incorporated by reference herein);

which is a Continuation of U.S. application Ser. No. 09/805,124, filedMar. 8, 2001 and entitled “Apparatus for Providing Redundant WirelessAccess to Field Devices in a Distributed Control System”, which issuedas U.S. Pat. No. 7,519,012 on Apr. 14, 2009;

which is a Continuation of U.S. application Ser. No. 08/864,750, filedMay 28, 1997, entitled “Distributed Control System for ControllingMaterial Flow Having Wireless Transceiver Connected to IndustrialProcess Control Field Device to Provide Redundant Wireless Access”,which issued as U.S. Pat. No. 6,236,334 on May 22, 2001;

which is a Continuation of U.S. application Ser. No. 08/782,513, filedJan. 9, 1997, entitled “Distributed Control System Having CentralControl Providing Operating Power to Wireless Transceiver Connected toIndustrial Process Control Field Device Which Providing RedundantWireless Access”, which issued as U.S. Pat. No. 5,682,476 on Oct. 28,1997;

which is a Continuation of U.S. application Ser. No. 08/483,119, filedJun. 7, 1995, and entitled “An Apparatus for Providing RedundantWireless Access to Field Devices in a Distributed Control System”, nowabandoned;

which is a Continuation-in-Part of U.S. application Ser. No. 08/328,324,filed Oct. 24, 1994 and entitled “An Apparatus for ProvidingNon-Redundant Secondary Access to Field Devices in a Distributed ControlSystem”, now abandoned.

BACKGROUND

This invention relates to accessing field devices in a distributedcontrol system. Specifically, this invention relates to providingredundant wireless access to such field devices remotely using wirelesstransceivers.

In a typical industrial plant, a distributed control system (DCS) isused to control many of the industrial processes performed at the plant.Typically, the plant has a centralized control room having a computersystem with user I/O, disc I/O, and other peripherals as are known inthe computing art. Coupled to the computing system is a controller and aprocess I/O subsystem.

The process I/O subsystem includes a plurality of I/O ports which areconnected to various field devices throughout the plant. Field devicesknown in the control art include various types of analytical equipment,silicon pressure sensors, capacitive pressure sensors, resistivetemperature detectors, thermocouples, strain gauges, limit switches,on/off switches, flow transmitters, pressure transmitters, capacitancelevel switches, weigh scales, transducers, valve positioners, valvecontrollers, actuators, solenoids, and indicator lights. As used herein,the term “field device” encompasses these devices, as well as any otherdevice that performs a function in a distributed control system and isknown in the control art.

Traditionally, analog field devices have been connected to the controlroom by two-wire twisted pair current loops, with each device connectedto the control room by a single two-wire twisted pair. Analog fielddevices are capable of responding to or transmitting an electricalsignal within a specified range. In a typical configuration, it iscommon to have a voltage differential of approximately 20-25 voltsbetween the two wires of the pair and a current of 4-20 milliampsrunning through the loop. An analog field device that transmits a signalto the control room modulates the current running through the currentloop, with the current proportional to the sensed process variable. Onthe other hand, an analog field device that performs an action undercontrol of the control room is controlled by the magnitude of thecurrent through the loop, which is modulated by the I/O port of theprocess I/O system, which in turn is controlled by the controller.Traditional two-wire analog devices having active electronics can alsoreceive up to 40 milliwatts of power from the loop. Analog field devicesrequiring more power are typically connected to the control room usingfour wires, with two of the wires delivering power to the device. Suchdevices are known in the art as four-wire devices and are not powerlimited, as are two-wire devices.

In contrast, traditional discrete field devices transmit or respond to abinary signal. Typically, discrete field devices operate with a 24 voltsignal (either AC or DC), a 110 or 240 volt AC signal, or a 5 volt DCsignal. Of course, a discrete device may be designed to operate inaccordance with any electrical specification required by a particularcontrol environment. A discrete input field device is simply a switchwhich either makes or breaks the connection to the control room, while adiscrete output field device will take an action based on the presenceor absence of a signal from the control room.

Historically, most traditional field devices have had either a singleinput or a single output that was directly related to the primaryfunction performed by the field device. For example, the only functionimplemented by a traditional analog resistive temperature sensor is totransmit a temperature by modulating the current flowing through thetwo-wire twisted pair, while the only function implemented by atraditional analog valve positioner is to position a valve between anopen and closed position, inclusive, based on the magnitude of thecurrent flowing through the two-wire twisted pair.

More recently, hybrid systems that superimpose digital data on thecurrent loop have been used in distributed control systems. One hybridsystem is known in the control art as the Highway Addressable RemoteTransducer (HART) and is similar to the Bell 202 modem specification.The HART system uses the magnitude of the current in the current loop tosense a process variable (as in the traditional system), but alsosuperimposes a digital carrier signal upon the current loop signal. Thecarrier signal is relatively slow, and can provide updates of asecondary process variable at a rate of approximately 2-3 updates persecond. Generally, the digital carrier signal is used to send secondaryand diagnostic information and is not used to realize the primarycontrol function of the field device. Examples of information providedover the carrier signal include secondary process variables, diagnosticinformation (including sensor diagnostics, device diagnostics, wiringdiagnostics, and process diagnostics), operating temperatures,temperature of the sensor, calibration information, device ID numbers,materials of construction, configuration or programming information,etc. Accordingly, a single hybrid field device may have a variety ofinput and output variables and may implement a variety of functions.

HART is an industry standard nonproprietary system. However, it isrelatively slow. Other companies in the industry have developedproprietary digital transmission schemes which are faster, but theseschemes are generally not used by or available to competitors.

More recently, a newer control protocol has been defined by theInstrument Society of America (ISA). The new protocol is generallyreferred to as Fieldbus, and is specifically referred to as SP50, whichis as acronym for Standards and Practice Subcommittee 50. The Fieldbusprotocol defines two subprotocols. An HI Fieldbus network transmits dataat a rate up to 31.25 kilobits per second and provides power to fielddevices coupled to the network. An H2 Fieldbus network transmits data ata rate up to 2.5 megabits per second, does not provide power to fielddevices connected to the network, and is provided with redundanttransmission media. Fieldbus is a nonproprietary open standard and isattracting attention in the industry.

As additional protocols and architecture gain popularity in theindustry, the industry will face greater and greater challenges meldingthese technologies together into a single distributed control system.For example, newer devices will be coupled to an existing distributedcontrol system. In these situations, the signals coming from the controlroom may expect traditional analog or hybrid technologies, but the fielddevices may be coupled to an H1 or H2 Fieldbus network. Conversely, thecontrol room of the industrial plant may be renovated, with the inputsand outputs to the control room comprising a modern H1 or H2 field bus,and the individual signals running to some older analog and hybrid fielddevices, and newer Fieldbus based field devices.

In addition to the challenge of integrating various technologies into asingle distributed control system, newer field devices will havemaintenance modes and enhanced functions that are not accessible via anolder control system. In addition, even when all components of adistributed control system adhere to the same standard (such as theFieldbus standard), one manufacturer's control room equipment may not beable to access the secondary functions or secondary information providedby another manufacturer's field devices.

SUMMARY OF THE DISCLOSURE

The present invention provides an apparatus for providing wirelessaccess to field devices in a distributed control system having a controlroom that, for example, provides hard-wired access to the field devices,thereby allowing access to the field devices in the event of a failurethe hard-wired media.

In a first embodiment, each field device is provided with a wirelessport and a hardwired port and can be accessed from a control room by awireless handheld unit or a wireless terminal. In one configuration ofthis embodiment, the wireless port is powered by the control network towhich the field device is connected.

In a second embodiment, a field module having a wireless port isconnected to an existing control network. The field module providesaccess from a wireless handheld unit or a wireless terminal in thecontrol room to all field devices connected to the control network. Inone configuration of this embodiment, the field module is powered by thecontrol network to which it is connected.

In a third embodiment, the distributed control system is provided with abridge that connects a distribution network in the distributed controlsystem to one or more control networks, wherein the control networks arecoupled to field devices. The bridge also includes a wireless port thatprovides access from a wireless handheld unit or a wireless terminal ina control room to all field devices connected to the control networks.

In still another embodiment, devices, such as field devices orinput/output devices within a process control system are provided withboth hardwired and wireless communication ports to enable communicationsto be performed within a process control system using one or both ofhardwired and wireless communications. In one case, a field device foruse in a process control system within a process control environmentincludes a microprocessor-based communication unit adapted to generateor receive communication signals, a first communication port adapted tobe connected to a hardwired communication link for providingcommunications to or from the communication unit via the hardwiredcommunication link and a second communication port adapted to beconnected to a wireless transceiver to provide wireless communicationsto or from the communication unit via the wireless transceiver.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a prior art distributed control system.

FIG. 2 is a diagram of industrial plant having two distributed controlsystems and shows three embodiments of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a block diagram of a prior art distributed control system(DCS) 10. DCS 10 is comprised of control room 12, controller 14,discrete/analog I/O unit 16, H2-to-H1 bridge 18, and a variety of fielddevices represented by solenoid 24, switches 26 and 54, valvepositioners 28, 46, and 52, transmitters 30, 34, and 44, processanalyzers 36 and 50. These devices represent any type of field deviceknown in the control art. Also shown in FIG. 1 are handheld units 38 and39, which are capable of accessing information in a hybrid orFieldbus-based field device via a physical wire connection, and a localoperator/user station 40, which is capable of communicating with fielddevice 30 over a physical wire connection.

Control room 12 includes computers, user I/O, various forms of datastorage devices, and other computing devices known in the art. Controlroom 12 is coupled to controller 14 via bus 20, which is typically aproprietary digital communications network or an open digitalcommunication network employing a proprietary protocol. Controller 14receives various commands from control room 12 and provides data tocontrol room 12.

As depicted in FIG. 1, DCS 10 is a hybrid system comprising twodifferent types of field devices. Devices 24-36 are traditional analog,discrete, and hybrid analog/digital devices, wherein the primary controlfunction of the device is realized by modulating a current. These fielddevices are coupled to discrete/analog I/O unit 16, with each deviceconnected to an individual channel of unit 16 by a single pair of wires(and possibly two additional power wires in the case of a traditionalfour-wire field device). For example, solenoid 24 is coupled viatwo-wire twisted pair 42 to channel 43 of unit 16.

For a traditional analog or discrete field device, the onlycommunication with the device occurs by modulating or switching thecurrent running through the two-wire twisted pair, with the magnitude ofthe current representing a measured process variable (as in the case ofthe transmitter), or an action requested by controller 14 (as in thecase of a valve positioner or solenoid). Traditional analog devices havea frequency response limited to approximately 10 Hz and receive powerfrom the two-wire twisted pair.

Hybrid analog/digital devices operate in a manner similar to traditionalanalog devices, but also allow digital communication of secondaryinformation by superimposing a digital carrier signal on the modulatedcurrent carried by the two-wire twisted pair. One such hybrid analogdigital system is known in the control art as Highway Addressable RemoteTransducer (HART) and transmits data in a manner similar to aconventional computer modem adhering to the Bell 202 specification.Generally, the primary function of these devices is still realized bymodulating the current through the loop, while other types of secondaryinformation, such as diagnostic data, operating temperature,identification codes, error codes, and secondary variables, aretransmitted digitally. In such a system, digital communication isrelatively slow and is limited to approximately 300 baud. When amaintenance person desires to test an analog device, the maintenanceperson must make a physical connection to the device itself, such aslocal operator/user station 40 connected to transmitter 30, or to thetwo-wire twisted pair leading to the device, such as handheld unit 38connected to the two-wire twisted pair leading to valve positioner 28.

In contrast, devices 44-54 are modem network-based digital fielddevices, wherein all information is digitally transmitted to and fromeach device. While many control system manufacturers have developedproprietary digital systems, the Standards and Practices Subcommittee 50of the Instrument Society of America has developed and specified anarchitecture known in the art as Fieldbus. The Fieldbus specificationincludes two types of networks, a lower speed network referred to as H1and a higher speed network referred to as H2. Both networks can supportmultiple connections to a single network bus, in contrast to traditionalanalog connections, which only support one device per two-wire twistedpair. While the present invention is described herein with reference toa Fieldbus network-based control system, in other embodiments thepresent invention may be employed in any distributed control systemhaving network-based field devices.

A Fieldbus H2 network can transmit data at a rate up to 2.5 megabits persecond. In addition, an H2 network includes two parallel sets ofphysical wire media: a primary wire media and a secondary, or redundant,wire media. Should the primary wire media fail, the secondary wire mediais automatically used by the DCS. Because of the high capacity andredundancy of H2 Fieldbus networks, H2 Fieldbus networks are beginningto be used as a distribution network that connect the controller tovarious distribution units in the DCS. However, traditional distributionnetworks are proprietary networks using either parallel or serialcommunication.

In FIG. 1, H2 distribution network 22 couples controller 14 to H2-to-H1bridge 18, and proprietary bus 21 couples controller 14 todiscrete/analog I/O unit 16. In other configurations known in the art,unit 16 and bridge 18 may be coupled to a common distribution network.As previously discussed, discrete/analog I/O unit 16 includes discretechannels, with each channel coupled to a single device.

H2-to-H1 bridge links the data carried by proprietary distributionnetwork 22 to H1 Fieldbus control networks 45 and 47. H1 Fieldbuscontrol network 45 is coupled to transmitters 44, valve positioner 46,and relay 48, and H1 Fieldbus 47 is coupled to process analyzer 50,valve positioner 52, and solenoid 54. While an H1 Fieldbus network lacksredundant wiring, and has a lower data transmission rate ofapproximately 31.25 kilobits per second, it is capable of providingpower to the devices to which it is coupled, while an H2 Fieldbusnetwork does not. For the above reasons, the H1 Fieldbus network isideal for providing final connections to individual field devices, whilethe H2 Fieldbus network is ideal for distributing control signalsthroughout the physical plant controlled by the DCS.

More recently, field devices have been provided with microprocessors andadditional functionality. Such “smart” field devices are capable ofmonitoring a plurality of process variables, performing a variety ofcontrol functions, performing comprehensive diagnostics, and providing awide array of various types of status information. The Fieldbusspecification specifies a variety of primary functions that may besupported by various Fieldbus field devices. In addition, manymanufacturers have provided secondary functions beyond those specifiedin the Fieldbus specification. While Fieldbus field devices manufacturedby different manufacturers are compatible to the extent that onlyFieldbus specified functions are accessed, they are not compatible withrespect to the secondary functions. For example, a Fieldbus controllermanufactured by company A will generally not be able to access thesecondary functions provided by a Fieldbus valve positioner manufacturedby company B. Therefore, an industrial plant using a variety of Fieldbuscomponents provided by different manufacturers will not be able to useof all the functions provided by the various components.

The problem is worse in older distributed control systems that weredesigned to use traditional analog/discrete and hybrid devices. Often acompany will wish to preserve an investment in an existing installation,and will retrofit the installation with newer Fieldbus field devices. Insuch an installation, the control room will not even be able to accessthe standardized Fieldbus functions provided by the various devices.Accordingly, a need exists to access the secondary functions provided byvarious manufacturers, as well as standardized Fieldbus functions when aFieldbus based device is connected to an older distributed controlsystem.

The present invention is an apparatus and method for providing redundantwireless access to field devices in a distributed control system,thereby allowing access to field devices in the event of a failure ofthe hard-wired media that connects the field devices to a control room.The redundant wireless access can be used several ways. First, it can beused to allow continued operation of a distributed control system duringfailure or maintenance of the hard-wired media. However, even ifcontinued operation is not desired, redundant wireless access may stillbe valuable for monitoring process variables and performing controlactions, such as those required to shut down a process. For example,consider a distributed control system subjected to an explosion. Theexplosion, may render the hardwired media connecting field devices tothe control room inoperable. Using the redundant wireless accessprovided by the present invention, a control room operator will still beable to access field device to perform an orderly shut-down of thedistributed control system. The operator may observe criticaltemperatures and pressures, and adjust or close valves and other devicesto complete the shut down. By having redundant wireless access to thefield devices, the operator may be able to effect a shutdown in such away as to minimize losses.

FIG. 2 is a diagram of an industrial plant having two distributedcontrol systems. DCS 56 is comprised of control room 60 (which includesterminal 104 coupled to wireless link module 106, which in turn isconnected to wireless transceiver 108), controller 62, bus 64, fielddevice 66, valve positioner 68, transmitter 70, process analyzer 72, H1Fieldbus control network 74, transmitter 76, valve positioner 78,solenoid 80, field module 82, and H1 Fieldbus control network 84. DCS 58is comprised of control room 86 (which includes terminal 103 coupled towireless link module 107, which in turn is connected to wirelesstransceiver 109), controller 88, bus 90, H2 Fieldbus distributionnetwork 94, H2-to-H1 bridge 92, transmitters 96 and 100, valvepositioner 98, and H1 Fieldbus control network 102. Buses 64 and 90 arenormally proprietary digital communication networks, or opencommunication networks employing a proprietary protocol.

Two embodiments of the present invention are illustrated in DCS 56. Thefirst embodiment is illustrated by those field devices coupled to H1Fieldbus control network 74. Each field device on control network 74includes a wireless transceiver. Field device 66 represents any genericfield device coupled to control network 74 and includes wirelesstransceiver 114. Valve positioner 68 includes wireless transceiver 116,transmitter 70 includes wireless transceiver 118, and process analyzer72 includes wireless transceiver 120. Each wireless transceiverimplements a redundant wireless Fieldbus connection with terminal 104,thereby allowing redundant wireless access to each field device fromcontrol room 60.

Another novel feature of the present invention is that the wirelessFieldbus port attached to each field device is powered by the hardwiredH1 Fieldbus port attached to each device. Since the wireless Fieldbuslink of the field devices is powered by the existing H1 Fieldbus controlnetwork, no additional wiring is required.

The wireless links disclosed herein represent any wireless communicationmethod known in the art, including, but not limited to, radio, infrared,visible light, and ultrasonic forms of wireless communication.

A second embodiment of the present invention is illustrated by thedevices connected to H1 Fieldbus control network 84. Transmitter 76,valve positioner 78, and solenoid 80 are each coupled to control network84. Also coupled to control network 84 is field module 82, whichincludes a wireless transceiver 122 powered by H1 Fieldbus controlnetwork 84. Field module 82, in essence, forms a wireless bridge betweencontrol network 84 and terminal 104 in control room 56, and allowsterminal 104 to access each device coupled to H1 Fieldbus controlnetwork 84. Accordingly, field module 82 is ideally suited for providingredundant wireless access in an existing environment having a variety ofH1 Fieldbus devices from different manufacturers.

A third embodiment of the present invention is illustrated by DCS 58. InDCS 58, controller 88 is coupled to H2-to-H1 bridge by H2 Fieldbusdistribution network 94. H2-to-H1 bridge links H2 Fieldbus distributionnetwork 94 to H1 Fieldbus control network 102. H2-to-H1 bridge alsoincludes a second Fieldbus port connected to wireless transceiver 124,and communicates with a remote device such as terminal 103. Accordingly,terminal 103 in control room 86 can access all field devices serviced bythe H2-to-H1 bridge, such as transmitters 96 and 100 and valvepositioner 98. In other configurations, it is common for an H2-to-H1bridge to service a plurality of H1 Fieldbus control networks, in whichcase all field devices connected to all control networks serviced by theH2-to-H1 bridge can be accessed remotely.

The present invention provides wireless redundant access to fielddevices in a distributed control system having a control room thatprovides hardwired access to the field devices. In a modem distributedcontrol system having Fieldbus devices coupled to a Fieldbus controlroom, the present invention provides a redundant wireless access to aterminal having a wireless link. The apparatus of the present inventionallows access to field devices in the event of failure or otherunavailability of the hard-wired media that couples the control room tofield devices.

In one embodiment, each Fieldbus-based device is provided with its ownsecondary wireless H1 or H2 Fieldbus port that is powered by the H1Fieldbus control network. This embodiment provides maximum flexibilitybecause no modification of the distributed control system is required,and is ideally suited for new devices that are to be added to anexisting Fieldbus installation. As soon as the H1 Fieldbus device isconnected to the existing H1 Fieldbus control network, the device can beaccessed via the wireless terminal.

In another embodiment of the invention, a field module is connected toan existing Fieldbus control network. The field module has a wireless H1or H2 Fieldbus port that is powered by the H1 Fieldbus control network,and provides access from the wireless terminal to all Fieldbus devicesconnected to the control network. This embodiment is ideally suited fordistributed control systems that already have Fieldbus devices.

In yet another embodiment of the present invention, the distributedcontrol system is provided with an H2-to-H1 bridge having one or more H1control networks coupled to Fieldbus devices, a hard-wired H2 portcoupled to a controller, and a wireless H2 or H1 Fieldbus port. Thewireless Fieldbus port allows a wireless terminal to access all Fieldbusdevices on all H1 control networks serviced by the H2-to-H1 bridge.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form in and detail without departing from thespirit and scope of the invention.

1. A distributed industrial process control system comprising: a centralcomputer system located in a control room and a first wirelesscommunication link associated with the central computer system fortransmitting and receiving process control information to and from thecentral computer system; and a field mounted controller located adistance from the central computer system; a plurality of processcontrol field devices; a process control network for communicatingprocess control signals between the controller and the plurality ofprocess control field devices, wherein at least one of the field deviceseither controls a physical process parameter based on a process controlsignal transmitted from the controller to the at least one of the fielddevices or measures a physical process control parameter and transmits aprocess control signal to the controller representing the measuredphysical process control parameter; and a second wireless communicationlink associated with the process control network for transmittingprocess control information to the central computer system and receivingprocess control information and secondary information from the computersystem.
 2. The system of claim 1, wherein the controller is adapted tocontrol the field devices based upon commands received from the centralcomputer system via the first and second wireless communication links,and adapted to provide data to the central computer system based uponsignals received from field devices via the first and second wirelesscommunication links.
 3. The system of claim 1 wherein the field devicesare powered from the process control network.
 4. The system of claim 1wherein the wireless communication link associated with the processcontrol network is powered from the process control network.
 5. Thesystem of claim 1 wherein the process control information includesprimary process control signals effecting physical process controlparameter controlled by a process control field device.
 6. The system ofclaim 1 wherein the process control information includes primary processcontrol signals representing a physical process control parametermeasured by a process control field device.
 7. The system of claim 1wherein the process control information includes secondary informationrelated to the operation of a process control field device.
 8. Thesystem of claim 1 wherein the central computer system is adapted tocommunicate with the controller through the wireless communication linksfor monitoring process variables.
 9. The system of claim 1 wherein thecentral computer system is adapted to communicate with the controllerthrough the wireless communication links for performing control actions.10. The system of claim 1 wherein the central computer system is adaptedto communicate with the controller through the wireless communicationlinks for performing diagnostics.
 11. The system of claim 1 wherein thecentral computer system is adapted to communicate with the controllerthrough the wireless communication links for accessing secondaryfunctions of the field devices.
 12. The system of claim 1 wherein thecentral computer system is adapted to communicate with the controllerthrough the wireless communication links for performing shut-downprocedures.
 13. A distributed industrial process control systemcomprising: a process control network; a plurality of industrial processcontrol field devices communicatively coupled to the process controlnetwork, wherein each of the plurality of field devices controls ormeasures a physical process parameter; a controller communicativelycoupled to the process control network for controlling the fielddevices, the controller producing process control information includingone or more control signals for causing one or more of the processcontrol field devices to control a physical process parameter accordingto the one or more process control signals, or receiving process controlinformation including one more control signals representing a physicalprocess parameter measured by one or more of the process control fielddevices; a remote process computer located a distance from thecontroller; and a wireless communication link between the processcontrol network and the remote process control computer forcommunicating process control information between the remote processcomputer and at least one of the controller or at least one of theprocess control field devices that are communicatively coupled to theprocess control network.
 14. The system of claim 13, wherein thecontroller is adapted to control the field devices based upon commandsreceived from the remote process computer via the wireless communicationlink, and adapted to provide data to the remote process computer basedupon signals received from field devices.
 15. The system of claim 13wherein the field devices are powered from the process control network.16. The system of claim 13 wherein the process control informationincludes primary process control signals effecting physical processcontrol parameter controlled by a process control field device.
 17. Thesystem of claim 13 wherein the process control information includesprimary process control signals representing a physical process controlparameter measured by a process control field device.
 18. The system ofclaim 13 wherein the process control information includes secondaryinformation related to the operation of a process control field device.19. The system of claim 13 wherein the remote process computer isadapted to communicate with the controller through the wirelesscommunication link for monitoring process variables.
 20. The system ofclaim 13 wherein the remote process computer is adapted to communicatewith the controller through the wireless communication link forperforming control actions.
 21. The system of claim 13 wherein thecentral computer system is adapted to communicate with the controllerthrough the wireless communication links for performing diagnostics. 22.The system of claim 13 wherein the remote process computer is adapted tocommunicate with the controller through the wireless communication linkfor accessing secondary functions of the field devices.
 23. The systemof claim 13 wherein the central computer system is adapted tocommunicate with the controller through the wireless communication linkfor performing shut-down procedures.